1. Technical Field
This invention relates to traffic control signaling in a fast packet network carrying Internet protocol packets and, more particularly, to the initiation of flow control signaling between layers one and two of a fast packet protocol such as the frame relay protocol and layers three, four or five of an Internet protocol such as the TCP/IP protocol upon receipt of a congestion message.
2. Description of the Related Arts
Referring to FIG. 1, there is shown an overview of a known fast packet network, for example, a frame relay or cell relay network, that is carrying packet data traffic between customer locations. By frame is intended a larger data carrying capacity within a single entity than a cell. A cell may comprise one or more data packets. The stacks 101 and 102 at the left and right respectively indicate stacks from the known open systems interconnect (OSI) model for describing layers of potential data transmission. Typically, customer applications software 103 runs on, for example, a personal computer workstation, labeled customer computer at location A or CCA and customer applications software 104 runs on the customer computer at location B or CCB. These talk to each other over the fast packet network at various levels of communication. The customer computer may be any intelligent communications terminal device having a controller and memory.
At level 1, there exists, for example, communication over a local area network (LAN) cable between the computer workstation CCA, CCB and the router 105, 106, for example, an ACT Networks SDM-9300 or other router known in the art. The router 105, 106 is connected via the customer""s CSU/DSU interface card 106, 107 to a time division multiplex (TDM) link to a comparable network""s CSU/DSU interface card 108, 109. Typically, the area of box 112 represents the facilities of an interexchange carrier 112 such as ATandT and are shown in greatly simplified form. At the edge of the IEC network may be a frame relay router 110, 111 which may, for example, comprise an ACT Networks SDM-9400 or SDM-9500 or other router known in the art. In between these edge switches, not shown, may be a satellite uplink, not shown and other intermediate switches.
At layer 3, is the Internet Protocol (IP) layer. The customer workstation CCA or CCB communicates with the respective router 105, 106. There is no Internet protocol or TCP protocol communication within the fast packet portion of the network 112. At layers 4 and 5, the TCP protocol operates and at layers six and seven, the http.ftp.telnet high level protocol operates. These layers are strictly between work stations CCA and CCB.
Consequently, starting at the 7 layer customer computer CCA or CCB, each stack of protocol can be understood as executing a software process on the individual network element depicted. For example, the complete 7-layer stack executing on the customer computer may, in actuality, be, for example, an inter daemon applications package 103 operating under the UNIX operating system or a comparable package operating under a Microsoft Windows operating system or other system known in the art to provide protocol-based end-to-end communications services. The flow of data in the network is from applications software 103 all the way across the network 112 to applications software 104.
The exchange of protocol-based control information in such a network is peer to peer. Fro example, if the TCP protocol processes on work station CCA exert flow control on the data stream, then it is exchanging flow control information with its peer TCP process on work station CCB. The same thing is true for IP and http and so on.
Now referring to FIG. 2, similar reference characters are used to denote similar elements. There is shown a similar figure emphasizing one end, for example, the CCA end of the network of FIG. 1 and with arrows shown designating what happens in the event of traffic congestion in the fast packet network. The X signifies the sensing of congestion at a frame relay switch within a fast packet network such as the ATandT frame relay network 112. A key at the top of the drawing indicates the interface between the IEC and the customer premises equipment.
Starting at the 7-layer customer computer CCA, outbound traffic traverses the router 105 and then may encounter congestion at the second network switch 201. When congestion is sensed in a fast packet network, it is known to originate congestion messages at level 2 in a forward and backwards network direction. The forward explicit congestion notification (FECN) message proceeds to the right (forward) and the backwards explicit congestion notification (BECN) message proceeds to the left (backward) by setting a bit within the cells or packets known as the FECN and BECN respectively to 1. For example, when congestion is noted, the forward message has FECN equal to 1 and BECN equal to 0. The backward message has FECN equal to 0 but the BECN equal to 1. Following the path of the BECN message, the message is passed by the edge switch 10 to the router 105. The edge switch 110 is not programmed at all to react to the BECN message. Presently, the router 105 strips or discards the BECN message. The router 105 is, like the edge switch 110, not presently programmed to react at all to the receipt of a congestion message. The fast packet protocols, including the frame relay protocol, are silent on what the end router is to do with the congestion message or any action to take. Congestion continues and dropped frames, cells and packets occur until the TCP layer finally senses longer acknowledgment times and/or missing packets. The TCP layer, being the first layer that is end-to-end or peer to peer is the first to react but is a layer that controls the presentation of data to the user at their work station and from the executing computer process 103 to the network. A layer 4 process may be executing on the router 105, but such a process is also typically passive to congestion at layer 2. Enhanced layer 4 functions are known, for example, firewall functions, but these are not flow control functions. In the typical case, the layer 4 router process is passive and so is not shown. In summary, it is believed that according to prior art processes, there is no slowing of data presentation to the network at workstation CCA even though network congestion is sensed at a frame relay switch 201 of the network and, eventually, frames (cells) are dropped due to the congestion.
Recently, the United States federal government has enacted legislation to encourage the delivery of Internet services to remote school districts, for example, that may only be reached by satellite. Examples of such school districts may comprise outlying Indian villages in rural Alaska, whose only telecommunications service is via satellite. Satellite introduces absolute delay into any data path due to the length of time it takes to travel to and from a geosynchronous satellite. Flow control becomes more acute because of this delay which would be experienced in a prior art flow control scheme where reliance on layer 4 TCP flow control measures is the only alternative. Data latency can consequently vary but may be typically increased from a latency on the order of a quarter to a half a second to a second to a second and a half. Latencies may typically be on the order of 900 milliseconds, so a fast reacting congestion alleviation scheme is desirable. Digital cell relay networks appear to be an economical and viable approach to providing such services and other data services as well such as telemedicine services at 56 or 64 kbps. It will be advantageous in the art if data flow control were provided in such networks especially those involving satellite links.
The obvious problem for customers of the interexchange carrier or other provider of frame relay services is dropped frames, cells or packets due to delays in implementing any data flow control. It is believed that there exists no method of signaling flow control between layer 2 and layer 4 from a network element to a network element. Consequently, TCP/IP traffic cannot flow smoothly or efficiently over a fast packet network, especially one involving satellite service delivery, according to the state of the art even though congestion sensing processes are known and congestion messages exist for signaling in a fast packet network.
The problems and related problems of the prior art flow control processes (as well as other types of control messaging) are solved according to the principles of the present invention by providing control signaling between layer 2 and layer 4 at a customer router. For example, in one embodiment, at an edge router or switch, the router is programmed to react upon receipt of a congestion message received from a switch within the fast packet network that has sensed a traffic congestion. The frame relay edge switch (or router) generates a request of the router to open a virtual control channel to the TCP layer on the customer router. As used in the claims and in the present description, router apparatus is intended to encompass either a router or a switch as is commonly used in the art. Once opened, the virtual control channel at the router is operative to throttle the congestion. The present application is associated with the initiation of the flow control signaling between the edge switch and the customer router. In the present application, the signaling path that is opened up will be referred to as a reverse pass through packet control channel to conform with the direction of congestion message described, that is, a backwards or BECN congestion message. By convention, an N+2 pass through packet channel request message received at a destination switch will operate in response to a FECN message to open a forward pass through packet control channel. If the edge switch passes through the BECN to the customer router, the router may be similarly programmed to react and open a control channel. Related concurrently filed applications, Ser. Nos. 09/223,053; 09/223,319; and 09/223,502 by the same inventor, Gregory D. Moore, hereafter incorporated by reference herein, discuss the operation of the router and the customer work station in response to the initial request which is referred to herein as an N+2 pass through packet (PTP) (N+2 PTP) request message.
Once the TCP virtual control channel is open, the edge switch (or customer router) then initiates an N+2 fair queue (N+2 FQ) message or control signal to signal the customer work station to xe2x80x9cslow downxe2x80x9d the presentation of packets to the network. The edge switch 110 or the router may generate the fair queue telemetry message which causes slow down of data egress to the edge switch 110 of the network. The established N+2 PTP channel allows the telemetry data to pass to layer 4 of the router 105 where the slowing down can occur. The layer 4 process on the router responds by slowing down the presentation of data to the network originating from layer 4 downward. The layer 4 process on the router then propagates a pass through packet xe2x80x9cslow downxe2x80x9d message to the layer 4 process executing on the customer work station. Frames may be buffered at the work station, the router or the edge switch. Receipt of a BECN causes slowdown of data ingress to the network. Frames inbound to the edge switch 110 from router 105 may be buffered at the edge switch 110.
Eventually, the congestion message BECN signaled by congested switch 201 to the edge switch 110 will clear; that is, the BECN bit will be restored to 0. This indicates an uncongested network condition and the edge switch generates an N+2 FQ control signal to speed up the presentation of data. The layer 4 process executing on the router responds by asking the work station to increase the rate of data presentation to the network. The router may also generate a pass through packet xe2x80x9cspeed upxe2x80x9d message to the layer 4 process executing on the customer work station. In the work station itself, it is suggested that a buffer memory be provided for storage of packets held for presentation to the network during periods of congestion. One possible memory area for such a purpose may be the unused video memory associated with the computer display.